1. Field of the Invention
The present invention relates to a method, particularly a multi-stage method, for sterilizing medical single-component or multi-component impression materials that can harden. Furthermore, the invention relates to an impression material that can be sterilized.
2. The Prior Art
Impression materials are used in great numbers and vary greatly in the number of components, the combinations of the individual components, or the method of curing.
Thus, for example, systems are used that cure by means of an addition reaction, such as addition-cross-linking silicone molding materials or corresponding polyether impression materials. Alternatively, condensation-cross-linking systems are used; condensation-cross-linking silicone and polyether impression materials will be mentioned as examples here.
Predominantly, these materials are used in two-component systems, which cure, i.e. harden after being mixed, in a more or less short period of time.
In medical uses, however, the problem often occurs that the material, which is in paste form initially, comes into contact with skin injuries or mucous membrane injuries or surgically exposed structures, in the mouth, or in endoprosthetics, in the case of hip joint prostheses or knee joint prostheses, whereby there is the risk that bacteria, fungi, or viruses will be transferred. This can lead to significant health impairments. Furthermore, the use of a sterile material that can harden can be necessary in dental medicine, for example as a root filler material.
Similar problems can also occur if the material as such is kept germ-free, but the objects used for its use, such as impression trays, mixers, or cartridge bodies, are not sterile and therefore carry germs.
For this reason, there is great interest in a sterile impression material and in sterile equipment for its application.
European Patent No. EP 1 477 151 A1 describes a sterilization method in which sterilization takes place by boiling at 100° C., or autoclaving takes place at 121° C. Also, sterilization with gamma rays, as well as the use of electron beams and X-rays, is proposed, but this can damage the impression material.
In European Patent No. EP 1 374 914 A1, a method is presented in which impression materials and/or their components are subjected to steam sterilization. In this connection, tins, tubular bags, tubes, syringes, and dual-chamber cartridges are used as so-called primary packaging, in which the components are contained. These are introduced into a sterilization packaging, together with accessories needed for application of the impression masses, such as mixing dies. This packaging with contents is then subjected to steam sterilization. In this connection, the temperature to be set amounts to preferably at most 138° C., according to European Patent No. EP 1 374 914 A1, and the duration of the method amounts to at most 30 minutes. According to EP 1 374 914 A1, the material can suffer irreparable damage due to longer reaction times and higher temperatures.
Another disadvantage of this method, i.e. the simultaneous sterilization of all of the components, in other words the masses to be cross-linked and the equipment used for this purpose, is that only conditions that can be tolerated by all the parts, with regard to their stability, can be applied. Parts that cannot be steam-sterilized, such as polyethylene closure caps, for example, otherwise suffer irreparable damage.
A similar concept is pursued by European Patent No. EP 1 374 915 A1. Here, the sterilization step takes place by irradiation sterilization. However, it is disadvantageous in this connection that addition-cross-linking silicone impression materials, in particular, already pre-cross-link at higher radiation doses, and therefore are no longer usable for any subsequent use for their intended purpose.